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12 June 2013

Your nose knows

Your sense of smell affects your behaviour, helps you to sense danger, and plays a subtle role in how you communicate with others.

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The smell of cinnamon brings back fond memories of your grandmother, and when you smell petrol fumes, you can't help getting flashbacks of the accident you were involved in years ago.

It's true: a whiff of a pleasant or unpleasant odour can take you on a trip down memory lane, and it could affect your emotions and mood. Part of this principle is employed in aromatherapy, where the aromas of different plant oils are used with the aim of healing body, mind and soul.

But while the jury is still out on whether aromatherapy really works, researchers are pretty sure that we've been underestimating our sense of smell all along. It affects our behaviour, helps us to sense danger, and plays a subtle role in how we communicate with each other.

How smell works

The root of your smelling mechanism lies in your body's limbic system: a complex system of nerve pathways and networks in your brain. The activities of your body that are governed by this system are those concerned with survival, the expression of fear, rage and pleasure, and the establishment of memory patterns.

This system is made up of the hippocampus, fornix, cingulate gyrus, hypothalamus, thalamus, amygdala and olfactory cortex. Although this might sound far too technical to be interesting, it's fascinating how your sense of smell actually happens and how it affects you.

When a smell enters your nasal cavity, it meets up with 1,000 different types of receptor neurons, which are located in the upper part of your nose and nasal septum. These receptors are specialised in such a way that some of them only react to certain smells.

The receptors then convert the smell into a message that's sent to the olfactory bulb in your brain, where it's partially processed. It's then passed onto other areas of your brain, which control emotions, behaviour and basic thought processes.

Thanks to this intricate system, some distant memories, for instance from your childhood, can only be recalled by smell.

Apart from the obvious functions, like helping us to taste food and to discern information about the chemical composition of substances before coming into direct contact with them, smell fulfils many other roles in the human body.

Interestingly, researchers have now found that one nostril sometimes detects scents slightly differently than the other. These subtle disparities in perception result from small differences in the time and intensity of a smell arriving at one nostril or the other.

Sensing danger?

Our sense of smell seems to sharpen when something bad happens.

Researchers from Northwestern University in the States recently proved this surprising connection by giving volunteers electric shocks while they sniffed novel odours.

Two bottles in a set contained the same substance and the third had a mirror image of it, meaning its odour normally would be indistinguishable. By chance, the volunteers correctly guessed the odd odour about one-third of the time.

Then the researchers gave the volunteers mild electric shocks while they smelled just the odd chemical. In later smell tests, they could correctly pick out the odd odour 70% of the time.

MRI scans showed the improvement was more than coincidence. There were changes in how the brain's main olfactory region stored the odour information, essentially better imprinting the shock-linked scent so it could be distinguished more quickly from a similar odour.

In other words, the brain seems to have a mechanism to sniff out threats.

Follow your nose

An American-Israeli study also found that people can be trained to rely exclusively on ground level smelling to successfully navigate unknown territory. In fact, we seem to instinctively mimic certain animal behaviours, including enlisting each nostril to independently identify distinct smells.

In this study, subjects were blindfolded and ear-plugged after being asked to follow a 10m trail scented with "chocolate essential oil". They followed the trail by moving close to the ground on their hands and knees and wearing thick gloves, with only their noses to guide them.

Two-thirds of the participants were able to do so. However, when their noses were plugged to cut off the ability to smell, none of them could follow the path.

Communication through smell
We often see communication through smell in animals. But did you know that humans also have olfactory communication skills?

Several research studies have shown that humans are able to produce and perceive pheromones – airborne molecules that are secreted by the glands in the skin. Our perception of these pheromones seems to be closely linked to attraction to possible mates, and it's believed that it plays a role in our sexual behaviour.

Pheromones are furthermore involved in synchronising menstrual cycles.

Aromatherapy: possible benefits

Certain aromas undoubtedly affect the brain in positive ways, and a few small studies have suggested that some aromatherapy oils could indeed have beneficial effects.

By means of electroencephalography (EEG), it's been shown that lavender oil leads to an increase in alpha waves, which are associated with relaxation. In the presence of alerting odours (for example jasmine), researchers have noted an increase in brain activity, whereas nutmeg, mace and valerian reduced systolic blood pressure and relieved stress in study participants.

More research needed

Although a lot of research has been done on how odours influence our physiology, much is still unexplained and calls for further scientific investigation.

In the meantime though, it can't hurt to surround ourselves with pleasant smells, and to pay more attention to this intriguing sense. Whether you enjoy the scent of pine kernels, orange peel, jasmine or simply the smell of your newborn baby, it probably has a much greater effect than you imagined possible.


Information sources:
- Fragrances and the Physiology of Man. (June 2009). Press release by Freebies PR & Marketing for www.essentialoils.co.za.
- How well we really smell. (December 2006). HealthDay News. http://www.health24.com/news/Ear_nose_and_throat/1-905,38719.asp
- Your nose can smell danger. (March 2008). HealthDayNews. http://www.health24.com/news/Ear_nose_and_throat/1-905,38719.asp
- Grammer, K. Fink, B. Neave, N. Human pheromones and sexual attraction. European Journal of Obstetrics & Gynecology and Reproductive Biology, Volume 118, Issue 2, Pages 135-142.

 
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